IR mirror.
An example of the element Gold

IR mirror.
Gold-surfaced mirror, probably for reflecting infrared light. Not sure why it's so thick, but maybe to dissipate heat and remain flat even while a lot of power is being reflected off it. That's just a guess though.Source:eBay seller rare-chips-4-uContributor:Theodore GrayAcquired:17 April, 2009Text Updated:17 April, 2009Price: $20Size: 2"Purity: 99%